Make sure the rootNode of a LiveNodeListBase is always a ContainerNode

Source/core/html/LabelsNodeList.h

Index: Source/core/html/LabelsNodeList.h
diff --git a/Source/core/html/LabelsNodeList.h b/Source/core/html/LabelsNodeList.h
index 8be1648f6ae17c896c64b67199ba23f5b05269c8..0c913a96945cf5216c43b7a21c91854508195a03 100644
--- a/Source/core/html/LabelsNodeList.h
+++ b/Source/core/html/LabelsNodeList.h
@@ -32,7 +32,7 @@ namespace WebCore {
 
 class LabelsNodeList FINAL : public LiveNodeList {
 public:
-    static PassRefPtr<LabelsNodeList> create(Node* ownerNode, CollectionType type, const AtomicString&)
+    static PassRefPtr<LabelsNodeList> create(ContainerNode* ownerNode, CollectionType type, const AtomicString&)
     {
         ASSERT_UNUSED(type, type == LabelsNodeListType);
         return adoptRef(new LabelsNodeList(ownerNode));
@@ -41,7 +41,7 @@ public:
     virtual ~LabelsNodeList();
 
 protected:
-    explicit LabelsNodeList(Node*);
+    explicit LabelsNodeList(ContainerNode*);
 
     virtual bool nodeMatches(const Element&) const OVERRIDE;
 };